The brain can be watched in action, but what actually causes conscious experience remains hard to test. Modern brain scans can track patterns of activity in real time, yet a basic question remains unanswered: which parts of the brain are responsible for awareness itself?
A technique known as transcranial focused ultrasound may help change that. The method enables researchers to non-invasively alter activity in precise regions deep within the brain, including areas that have long been inaccessible in healthy individuals. In a recent paper published in Neuroscience & Biobehavioral Reviews, researchers outline a roadmap for using the technology to test where conscious perception is generated by directly probing brain circuits.
“It truly is the first time in history that one can modulate activity deep in the brain, centimeters from the scalp, examining subcortical structures with high spatial resolution,” said Daniel Freeman, an MIT researcher and co-author of a new paper on the subject, in a press release. “There’s a lot of interesting emotional circuits that are deep in the brain, but until now you couldn’t manipulate them outside of the operating room.”
Why Consciousness Is So Difficult to Study
Much of what researchers know about consciousness comes from observation. Brain imaging can show which regions become active during vision, pain, or decision-making, but activity alone does not reveal whether a region is producing a conscious experience or simply responding to one.
That limitation has left room for competing ideas about how consciousness works. Some theories suggest that conscious experience relies on higher-level mental processes, such as reasoning, self-reflection, and the integration of information across multiple brain regions. In this view, awareness emerges from large-scale networks, often involving the frontal cortex.
Other theories propose that conscious experiences arise more directly from specific patterns of neural activity, without the need for complex cognitive processing. From this perspective, consciousness may be generated in more localized regions, including sensory areas at the back of the cortex or deeper, subcortical structures.
“There are very few reliable ways of manipulating brain activity that are safe but also work,” said Matthias Michel, an MIT philosopher who studies consciousness and co-authored the new work.
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Testing Competing Theories of Consciousness
The roadmap outlined in the paper is designed to move these debates beyond theory. Transcranial focused ultrasound allows researchers to selectively alter activity in targeted brain regions while participants perform perceptual tasks, creating an opportunity to test which regions are actually necessary for conscious experience.
If awareness depends on higher-level cognitive processing, then disrupting activity in frontal or integrative regions should affect perception in measurable ways. If, instead, consciousness arises from more localized or deeper neural activity, then altering those regions should change what a person perceives even when higher-level areas remain intact.
Because focused ultrasound can reach several centimeters below the surface of the brain, it makes it possible to test the role of subcortical structures that have long been difficult to study non-invasively. That capability is central to the paper’s aim of turning long-standing questions about consciousness into experimentally testable ones.
What This Could Reveal About How Consciousness Works
Beyond testing theories of consciousness, the researchers suggest that transcranial focused ultrasound could help clarify how different brain regions interact over time to produce a unified experience. Conscious perception unfolds across milliseconds, yet depends on signals moving between distant parts of the brain. Being able to briefly alter activity in one region while leaving others untouched could help reveal how those signals are coordinated.
The approach may also complement existing brain-imaging methods. By combining focused ultrasound with tools like EEG or functional MRI, researchers could link changes in neural activity directly to changes in perception, creating a more complete picture of how conscious experience emerges moment by moment.
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Article Sources
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- This article references information from a new study that was published in Neuroscience & Biobehavioral Reviews: Transcranial focused ultrasound for identifying the neural substrate of conscious perception
